diff --git a/sys/dev/acpica/acpi_battery.c b/sys/dev/acpica/acpi_battery.c
--- a/sys/dev/acpica/acpi_battery.c
+++ b/sys/dev/acpica/acpi_battery.c
@@ -330,7 +330,7 @@
 
     /* NUL-terminate the string if we reached the end. */
     if (i == len)
-	*str = '\0';
+	*(str - 1) = '\0';
 }
 
 /*